Process for the manufacture of high purity cyclopentene

ABSTRACT

A TWO-STAGE HYDROGENATION AND SEPARATION PROCESS OF A CYCLOPENTADIENE SOURCE FOR THE MANUFACTURE OF A SUBSTANTIALLY DIOLEFIN FREE, HIGH PURITY CYCLOPENTENE SUITABLE FOR POLYMERIZING.   D R A W I N G

Feb. 23, 1971 D. C. TABLER T PROCESS FOR THE 'HKNUFACTURE OF HIGH PURITY CYCLOPEN'I'ENE Filed Dec. 22, 1969 IO I INVENTORS D. C. TABLER MMJOIjNSON BY United States Patent Ofice 3,565,963 Patented Feb. 23, 1971 3,565,963 PROCESS FOR THE MANUFACTURE OF HIGH PURITY CYCLOPENTENE Donald C. Tabler and Marvin M. Johnson, Bartlesville,

kla., assignors to Phillips Petroleum Company, a corporation of Delaware Filed Dec. 22, 1969, Ser. No. 887,286 Int. Cl. C07c 3/00 US. Cl. 260-666 3 Claims ABSTRACT OF THE DISCLOSURE A two-stage hydrogenation and separation process of a cyclopentadiene source for the manufacture of a substantially diolefin free, high purity cyclopentene suitable for polymerizing.

This invention relates to a process for the manufacture of high purity cyclopentene. In one aspect the invention relates to manufacturing a high purity cyclopentene suitable for polymerization.

The art suggests production of cyclopentene from cyclopentane as well as from cyclopentadiene or dicyclopentadiene. cyclopentadiene being commercially available as a by-product of the petroleum industry has been converted into cyclopentene by being subjected to a selective hydrogenation process. Even though cyclopentene of high purity has been achieved by the art, problems still exist since small amounts of diolefins remain as a contaminant in the partially purified cyclopentene. The remaining impurities of diolefins prevent such partially purified cyclopentene streams from being used in certain polymerization procedures.

It is an object of this invention to manufacture a substantially diolefin free, high purity cyclopentene.

It is another object of this invention to manufacture a cyclopentene of polymerization grade purity.

Heretofore, none of the methods available in the art have been able to provide a high purity cyclopentene from a cyclopentadiene stream without the remaining diolefins resulting in an undesired contaminate concentrate. The contaminates consist essentially of piperylenes and any unreacted cyclopentadiene since they both have similar boiling points to that of cyclopentene, therefore they concentrate in the cyclopentene when the mixture is distilled. Even though they are present in very small amounts in the partially purified cyclopentene, their removal continues to present a challenge.

We have discovered an improved method for the production of high purity cyclopentene from the cyclopentadienes existing in cracked gasoline or other pyrolysis products such as debutanized aromatic concentrate. Selective hydrogenation of the included cyclopentadiene of these feedstreams by this invention produces a high purity polymerization grade cyclopentene through a two-stage hydrogenation and fractionation process. In the first stage, the majority of the cyclopentadiene is converted to cyclopentene. But the remaining, similar boiling diolefins must be removed from the concentrated cyclopentene by the second stage hydrogenation-fractionation.

The major purpose of the second hydrogenation of the cyclopentene concentrate is to make sure that substantially all of the diolefins are removed. These diolefins, for example, include piperylenes, isoprene and cyclopentadiene. The diolefin removal is measured by the Maleic Anhydride Value which drops from a value of above 35 following one hydrogenation-fractionation stage to a value of less than 2 following the second hydrogenation-fractionation stage of this invention. The Maleic Anhydride Value method provides an estimate of the conjugated diolefins in hydrocarbon mixtures boiling in the gasoline range. The Maleic Anhydride Value may be defined as the number of milligrams of maleic anhydride which reacts with one gram of sample.

We have found that high purity cyclopentene can be produced by the selective hydrogenation of cyclopentadiene contained in a naphtha cracker C cut or the liquid by-products of ethylene units. These streams always contain diolefins as example, piperylenes. We have found when working with debutanized aromatic concentrate or a naphtha cracker C cut, that a small concentrate of diolefins remains unhydrogenated after the first hydrogenation stage. When the cyclopentene is recovered by distillation the unhydrogenated diolefins, mostly piperylenes, will be concentrated in the cyclopentene stream since they boil at almost the same temperature as does cyclopentene. It is a estimated that the cyclopentene stream could contain up to 4 weight percent of these unhydrogenated diolefins following the first stage hydrogenation and fractionation. We have found that if the cyclopentene concentrate is hydrogenated at milder hydrogenation conditions, the diolefins are converted to monoolefins, for example, the piperylenes are converted to n-pentenes, which are easily removed by distillation, correspondingly only a small fraction of the cyclopentene is hydrogenated to cyclopentane under these milder hydrogenation conditions.

Essentially diolefin-free, high purity, cyclopentene is in demand as the monomer for the production of an unsaturated polymer of cyclopentene. Polymerization grade cyclopentene should be at least 99 mol percent pure with a diolefin content of no more than 600 ppm. in the concentrated cyclopentene.

A typical debutanized aromatic concentrate stream from an ethylene unit will contain about 10 to 20 percent by weight cyclopentadiene-dicyclopentadiene in an equilibrium state. A typical C refinery cut from a naphtha cracker contains about 3 to 7 weight percent cyclopentene and about 25 to 35 weight percent cyclopentadiene. By

the application of the method of this invention high purity yields of cyclopentene are achieved. Other petrochemical by-products, for example methylcyclopentene, benzene, toluene and/ or xylenes, are also formed.

The method of our invention takes, for example, a fresh Referring to the drawing, a fresh feedstream 2 is mixed with the stage 1 liquid recycle stream, '4, the stage 1 vapor recycle stream 6, and the stage 1 makeup hydrogen stream 8 resulting in the stage 41 feedstream 10. The stage 1 feedstream 10 is fed into the hydrogenation feedstock of about 64 weight percent diolefins and dilutes reactor 11, producing a stage 1 eflluent 12. The stage 1 it with recycle olefins to lower the diolefin content to about fil ent 12 is Separated in separator 13 into a liquid stage weight percent in order to limit the heat rise across the 14 and a vapor stage 16. Parts of both the vapor and first stage reactor to about 80 F. Controlling the first the q id phases f the separator 13 are recycled to the stage heat rise with nonreactive recycle olefins diluent pro- 10 Q The remaining q d Product of the Separator vides for a more satisfactory conversion of cyclopenta- 13 1S Introduced fractlohatlon towel 17 Producing a diene to cyclopentene with a minimal conversion of cyclop Stream separatloh of cohflehtrated cyclopentene pentene to cyclopentane. The mixture is selectively hyand a bottom Stream Separation of benzene-toluene drogenated in the vapor phase at about 100 p.s.i.g. and F The Concentrated cyclopentene Stream 21 an approximate temperature range of 480 to 560 F. 1S mlxed Wlth the Stage 2 Vapor recycle Stream and over a nickel sulfide on alumina catalyst. Hydrogen is the Stage 2 makeup hydrogen stream 24 resultmg 1n the added to the feed at a rate of one mol of hydrogen per Stage 2 feedstream 26. Stream 26 is introduced to the hymole of hydrocarbon, giving about 3 mols f hydrogen drogenatlon reactor 27 WhlCh produces the stage 2 efliuent per mol of diolefin present in order to convert as much of Stream The 3 2 effluent Stream 28 1s sepalatd the diolefin contaminate as possible to monoolefins. The Separator 29 whlch Ylelds a total Vapor Phase Stream 30 cyclopentene Stream from the first h d ti f and a hydrogenated cyclopentene concentrate stream 32. tionation stage contains about 1 Weight pfircent of Stream 32 is fed to the fractlonatlng tower 33 which proreacted diolefins which are essentially removed in the dhces a P Stream 4 f hlgh purity cyclopentene and a sficond hydrogenation Stage bottom stream 36 of cyclopentane, methylcyclopentene,

The unreacted hydrogen is separated from the first and benzenestage hydrogenation eflluent by cooling to about 100 F. EXAMPLE I so that about 50 weight percent of the total efilu n A cyclopentadiene containing debutanized aromatic condenses- The unconfiensed p l conslstlng 0f Y Q P centrate (D.A.C.) stream from an ethylene unit could Ihethahe and a l Portloh of hydrocarbons cohtalhlhg produce the following feed, single hydrogenation and twohve Carbon atoms p molecule, 18 comprfissed and stage hydrogenation by weight percent yields as shown in cycled to the first stage hydrogenation reactor. The higher Table 11 the first stage hydrogenation operating pressure, the TABLE II lower the amount of C hydrocarbons which will be left I H Single In two stage in the recycle hydrogen, the lower the recycle compressor- D.A.C'. hydiogenahydrogenacompression ratio and consequently the lower the comfeed pression work required. But the higher reactor operating t-Butene-2 pressure produces a greater formation of polymers so gjg g g Z 8-8 that as a compromise approximately 100 p.s.i.g. is chosen 2-methylbutene 1 0:0 as the first stage inlet pressure. A portion of the recycle i Q1 9 g hydrogen stream 15 vented to prevent an undue bulld- 40 c-Pentene-2 0.33 0. 03 up of methane statement 3- "61' 012 The second stage hydrogenates substantially all the di- 0:211 013 2.1 olefins remaining in the first stage cyclopentene product 3:3? 8-2 under milder, more selective hydrogenation conditions. 2.23} 0:0 The temperature range of the second hydrogenation stage oyclopgrltadiene plus dicydm 7 is approximately 450 to 500 F. with only about a 10 entttdlene 0.0 F. temperature rise occurring across the reactor due to %g{ f 8-8 the small amount of reactive diolefin present. Under these Other coiupohntst: 0: 0 milder hydrogenation conditions, only a small amount of ,Pwbamy Cd olefins and cycloolefins cyclopentene 1s converted to cyclopentane. About 1.7 weight percent of the cyclopentene is converted to cyclo- EXAMPLE II pentane, but this small conversion is tolerated since sub- A C cut from a naphtha cracker containing about 3 stantially complete diolefin conversion occurs. to 7 weight percent cyclopentane and 25 to 35 Weight per- The broad and preferred operating conditions for the cent cyclopentadiene could produce the following feedtwo-stage hydrogenation process of this invention are stream material balance in pounds per hour as shown in given in the following table: Table 11.

TABLE I Operating Operating conditions conditions in the in the first recator second recator Catalyst composition Broad Preferred Broad Preferred Broad Preferred Percent nickel Catalyst base 1 Calcium aluminate magnesium oxide.

8-12. Activated alumina Activated alumina. 

